Project Summary The life of patients with Cystic fibrosis (CF) continues to be shortened by progressive lung disease. Recently, the development of specific small molecules that rescue mutation specific CFTR function have made remarkable impacts on patient care, but they are not available for many patients. In addition, ongoing airway inflammation may reduce their effectiveness, at least in some patients. In this context, TGF-b1, a cytokine associated with worse pulmonary outcome in CF, decreases airway surface liquid (ASL) volume in CF cells in vitro by impairing the function of calcium activated chloride channels (CaCCs) and the apical potassium channel BK, both crucial for maintaining ASL volume in CF. TGF-b1 also reduced mucociliary clearance in sheep. We therefore propose that airway inflammation in general and TGF-b1 in particular worsens mucociliary function in CF patients. If this hypothesis is correct, novel anti-inflammatory medications could improve CF outcomes in patients currently not eligible for CFTR recovery therapy on which we focus here, but might also improve the function of small molecules. Clinically used Angiotensin II Receptor Blockers (ARBs) inhibit TGF-b signaling, independent of their angiotensin receptor blocking ability. Losartan, one widely used ARB, exerts these latter effects through one of its major metabolites, EXP3179. Thus, ARBs could present a ?fast track approach? for improving mucociliary dysfunction in CF. The preclinical, in vitro proof of concept aim 1 will test the hypothesis that losartan reverses the negative effects of TGF-b1 on CaCC and BK function (BK mainly through preventing decreases in LRRC26, the g regulatory subunit of BK required for its function in non- excitatory cells). Mechanisms of losartan's actions on CaCC and BK function will be explored using Ussing chambers as well as ASL volume and mucus transport measurements in fully differentiated airway epithelial cells from CF patients in the presence or absence of TGF-b1, losartan, and its metabolites EXP3174 and 3179. The preclinical, in vivo animal model aim 2 will test the hypothesis that inhaled or oral losartan improves CF- related mucociliary dysfunction in sheep induced by inhaled CFTRinh172 and human neutrophil elastase (HNE) or TGF-b1, which is downstream of HNE. We will measure tracheal mucus velocity, determine key pharmacokinetic parameters of losartan, and explore mechanisms that induce mucociliary dysfunction. Finally, the clinical in vivo aim 3 will test the hypothesis that oral losartan improves mucociliary dysfunction and decreases airway and systemic inflammation in CF patients who are not on small molecule treatment. The proposed experiments will test the ability of available anti-inflammatory medications, namely losartan and its metabolites, to improve parameters of mucociliary function in CF in vitro and in vivo and delineate their mode of action, thereby potentially identifying a ?low-hanging-fruit? intervention for CF airway inflammation.